1. Field of the Invention
The present invention relates generally to a conveyer system used in industrial production lines and so forth. More specifically, the invention relates to a so-called free-flow type roller conveyer system application for a production line requiring high precision and high accuracy in production, such as IC chip production lines and so forth.
2. Description of the Background Art
One of the typical free-flow type conveyer systems is known as a roller-chain type conveyer system. This type of conveyer system employs an endless chain which carries a plurality of idler rollers arranged at regular intervals. An object to be conveyed is mounted on an idler roller and carried according to the chain drive. Since the object is mounted on an idler roller, the movement of the object can be stopped by exerting a small resistance or movement restricting force. Therefore, in practical operation, the object can be held at respective stations in the production line for manufacturing operations. However, in such a system, the chain and rollers are continuously driven even while the object is stopped at a station. This inevitably causes a vertical vibration of the object at a stopped position to interfere with or make it difficult to perform the required production operation. When the treatment required at the production station requires a high degree of precision, such vertical vibration becomes a particularly critical problem.
In order to solve such problems in roller-chain type conveyer systems, there has been proposed a roller drive type conveyer system which drives the object by the rotating torque of a plurality of driven rollers stationarily installed along the conveying path and driven by means of a driving means in a feed direction. In such types of conveyer systems, since the conveying force is exerted onto the object simply by the surface-to-surface friction between the object and the periphery of the driven roller, the object can be easily stopped at a production station. Each driven roller in this type of conveyer system is rotatably supported on a roller shaft extending from a stationary support frame. The roller is connected to a driving means, such as a driving motor via an endless drive belt which transmits the driving torque. In this construction, a substantially high accuracy of respective components of the conveyer system is required in order to eliminate vibration of the object which would otherwise be caused due to production errors in respective components. However, as will be appreciated, it is not practically possible to provide satisfactorily high accuracy in production of respective components of the conveyer line and thus is not possible to suppress the vibration of the object to a satisfactory level.